A group of Catholic priests opposed to church modernisation has condemned World Youth Day as an appalling display of secularism with little holy or Catholic content.

The priests, from the Holy Cross Seminary in the New South Wales town of Goulburn, are members of the Society of St Pius the 10th, which is opposed to innovations that followed the Second Vatican Council.

In a sharp rebuke of World Youth Day festivities in Sydney, Holy Cross Rector Father Peter Scott said World Youth Day did nothing to help prepare the way for Catholics to reach heaven.

"The reason I'm not in favour of World Youth Day is because of what happens and what has consistently happened since it was initiated by Pope John Paul II," Father Scott told AM.

"It has become an occasion for a very secular approach to religion, it's become just a happy party - a week of partying and concerts and world activities with very little that is truly holy and sacred and prayerful and Catholic for that matter," he said.

World Youth Day events in Sydney have been characterised by overt displays of joy described by observers as more akin to a rock concert than organised religion, with parties and other festivities a feature of the program.

Along with the spiritual aspects of the event, the social interaction that comes with hundreds of thousands of young people mingling is also a big attraction for the pilgrims.

"Just the euphoria of everyone coming together, all different countries for one purpose, for peace," said one young female pilgrim.

"It's a good time because you can do so many things you don't expect to be doing and there's great people, you can be doing partying when you don't expect to," said a young male participant.

Father Scott is sharply opposed to the strong secular atmosphere around the event.

"They'll have a few masses, a few experiences, but they'll be very liberal, easy-going, secular unsacred kinds of things.

"We consider ourselves, that we are the mainstream. We are the true Catholics.

"We are doing what the church has always done. We follow Catholic tradition, we have the traditional mass only, and every other traditional liturgical and spiritual practice which is necessary to sanctify our lives on this earth and go to heaven," he said.

The Society of St Pius the 10th has around 20 churches in Australia. Father Scott estimates it has around 3,000 adherents.

Catholic commentator Paul Collins says the group is extremist, out-of-date and isolated.

"In a way they want to live in a kind of a cultural cul-de-sac. They're kind of almost self-imprisoned. And it's sad to see that because many of them are very good people, many of them are very sincere and committed people," he said.

You have no doubt been hearing a lot about the Paris Agreement and know that it pertains to climate change, but are too embarrassed at this stage to ask for an overall explanation of what it's all about.